(a) Field of the Invention
The present invention relates to an electronic shutter of a camera, and more particularly, to a driving method and device for an electronic shutter used in cameras which (a) reduce the focus control time by minimizing the focus control lens movement necessary for focusing according to the distance to a subject; (b) maintain an optimal exposure by reducing temperature variations of the camera during the sector opening; and (c) provide a reliable focus control throughout the entire focal distances by electronically compensating for assembly defects.
(b) Description of the Related Art
Cameras using an electronic shutter typically have a system that conducts automatic focus control by adjusting focus control lenses to correspond to distances between the camera and the subject and performs automatic exposure by controlling the opening size of a diaphragm according to the light levels.
Conventional cameras utilizing such electronic shutters are disclosed in U.S. Pat. Nos. 4,918,480, 4,634,254 and 5,111,230; and Japanese Patent No. Showa 61-9632.
With reference to FIGS. 12, 13a-c and 14, U.S. Pat. No. 4,918,480 discloses an invention wherein a clockwise rotation of a step motor 216 moves a second rotating member 223 against a first rotating member 222, which is a focus control ring and directly contacts the second rotating member 223. At the same time, the stopper 239 moves along the gear portion 236 of the second rotating member 223 one tooth at a time until the first rotating member 222 reaches the focused zoom location calculated by the electronic controller (not shown).
When the first rotating member 222 reaches the focused zoom location, the step motor 216 rotates counterclockwise and the second rotating member 223 moves in the opposite direction to open a sector to a degree of exposure calculated by the camera's electronic controller. At this point, the second rotating member 223 is held at the zoom location by the stopper 239. Further, after opening the sector corresponding to the determined degree of exposure, the step motor 216 then again rotates clockwise to close the sector.
Even after the sector has been completely closed, the second rotating member 223 continues to rotate to come in contact with the first rotating member 222. Accordingly, the first rotating member 222 completes its rotation to the determined zoom location, and the stopper 239 moves to the end of the gear portion 236 of the second rotating member 223, where the stopper 239 becomes disengaged from the gear portion 236. When the stopper 239 is disengaged from the gear portion 236, the step motor 216 rotates in the counterclockwise direction, returning the entire system to an initial state.
With reference to FIG. 15, U.S. Pat. No. 5,111,230, discloses an invention wherein a clockwise rotation of a step motor has a main drive ring 304 rotate counterclockwise to move a lens drive ring 305 (304b pushes against 305c). As a result, a latch lever 308 passes over latch gears 305e one tooth at a time.
When the lens drive ring 305 reaches a zoom location determined by a camera's electronic controller (not shown), the step motor then rotates counterclockwise. At this time, although the lens drive ring 305 is forced to rotate counterclockwise by a spring 306, the latch lever 308 engaged with the latch gears 305e prevents the lens drive ring 305 from moving and maintains its position where zooming is completed.
When zooming is completed as calculated by the electronic controller and the step motor starts to rotate counterclockwise, a trapezoid cam 304d of the main drive ring 304 is located to the left of a protruding trigger arm 316b. Here, even if the trapezoid cam 304d contacts the protruding trigger arm 316b by the counterclockwise rotation of the main drive ring 304, the protruding trigger arm 316b merely rotates clockwise and a sector open/close lever 310 remains locked.
The counterclockwise rotation of the step motor rotates the main drive ring 304 clockwise and the trapezoid cam 304d of the main drive ring 304 contacts the protruding trigger arm 316b. Here, the rotational force of the main drive ring 304 passes through the trigger arm 316b and is transmitted to a pin 313b of a hold lever 313. Accordingly, the hold lever 313 rotates counterclockwise.
The counterclockwise rotation of the hold lever 313 releases the sector open/close lever 310 and the lever 310 rotates clockwise by the elastic force of a spring 315, thereby opening a sector. As soon as the sector opens, the step motor stops rotation and keeps the sector open for a period corresponding to a degree of exposure calculated by the camera's electronic controller.
Then, the step motor continues to rotate counterclockwise such that a first projection 304c of the main drive ring 304 pushes against a lower portion of the open/close lever 310, thereby closing the sector. Further, the second projection 304b of the main drive ring 304 pushes upward on an extension 308b of the latch lever 308 such that the lens drive ring 305 is released to move free. Accordingly, the lens drive ring 305 rotates clockwise by the elastic force of the spring 306 to return to the initial position.
In U.S. Pat. No. 4,634,254, with reference to FIG. 16, a focus control lever 407' remains unlocked by an active magnet while a step motor rotates clockwise from an initial position. From this state, a distance ring 409' moves in unison with a drive plate 401' by the elastic force of a spring 409'f until the distance ring 409' reaches a zoom position calculated by the camera's electronic controller (not shown). When the distance ring 409' reaches the zoom location, the magnet is turned off to lock the focus control lever 407', thereby also keeping the distance ring 409' locked.
The step motor continues to rotate clockwise even after the distance ring 409' is locked and rotates a sector lever 404' along the shape of the drive plate 401' to open a sector for the exposure period calculated by the camera's electronic controller. After opening the sector, the step motor rotates counterclockwise and the sector lever 404' follows the shape of the drive plate 401' by the elastic force of the spring 409'f, thereby closing the sector. A continued counterclockwise rotation of the step motor returns the entire system to the initial state.
The zooming of a focus control lens by the movement of the distance ring 409 in U.S. Pat. No. 4,634,254 will be described hereinafter with reference to FIG. 17.
Through first release and second release operations, the drive plate 401' moves the focus control lens from a minimum zoom location (j) to a maximum zoom location (k). The focus control lens is mechanically locked when it reaches a position corresponding to the subject distance. Then, the drive plate 401' rotates in an opposite direction to perform an exposure operation for a specific period determined by the camera's light meter. Then, the focus control lens returns to the minimum zoom location (j), which is an initial state.
The minimum zoom location (j) refers to the focus control lens position when focused for the maximum distance to the subject and the maximum zoom location (k) refers to the focus control lens position when focused for the minimum distance to the subject.
In Japanese Patent No. Showa 61-9632, with reference to FIG. 18, a step motor 503 rotates clockwise in an initial state to move a drive plate 501 to the right. Simultaneously, an active electromagnet 507e attracts a steel piece 507c to keep a focus control lever 507 disengaged from teeth 502c.
An extension 502e of a focus control distance ring 502 contacts a projection 501d of the drive plate 501, and the focus control distance ring 502 rotates clockwise to zoom a picture lens. When the focus control distance ring 502 reaches a position determined by the camera's electronic controller (not shown), the electromagnet 507e is deactivated by cutting off the power supply. Accordingly, the focus control lever 507 rotates clockwise by the elastic force of a spring 507a. Thus, a hook 507d of the focus control lever 507 engages with the teeth 502c of the focus control distance ring 502 to prevent it from moving and keep the picture lens focused.
Next, the step motor 503 rotates counterclockwise to move the drive plate 501 to the left. And the counterclockwise rotation of the sector lever 504 by a cam 501f and the elastic force of a spring opens a sector. The sector opens until a level of exposure, determined by the camera's electronic controller, is reached. And the step motor 503 again rotates clockwise to move the drive plate 501 to the right. Accordingly, the sector lever 504 rotates clockwise until the sector is closed, and the drive plate 501 continues to move to the right until it reaches the initial position.
Each of the above conventional electronic shutter systems provides a rotating ring that moves a focus control lens according to the measured distance to a subject and a locking mechanism that locks the rotating ring when the focus control lens has reached the focus position. Further provided are sector open/close means for first opening the sector for an amount of time corresponding to a level of exposure determined by the camera's electronic controller, then closing the sector; a return mechanism for returning an exposure control ring to an initial position, the exposure control ring operating the sector open/close means until an established position is reached by the sector; and a power source, providing power for the operation of the rotating ring, exposure control ring and the locking mechanism.
Accordingly, cameras using such conventional electronic shutters have a complicated structure to drive the focus control lens. Further, while focusing and controlling exposure for different subjects, the rotating ring moves the focus control lens from a minimum distance to a maximum distance and vice versa which increases the zooming time.
In addition, a now very common practice in conventional cameras using such an electronic shutter is to put multiple steps between the minimum and maximum zoom locations to enhance focus control. In such methods, since the focus control ring must rotate from an initial position to a specific position to control the focus, it takes longer to control the focus and the responsiveness of the electronic shutter is reduced.